This present application relates generally to apparatus, methods and/or systems for improving the heat exchanging or convective cooling characteristics within the hollow passages of machine parts or components. More specifically, but not by way of limitation, the present application relates to apparatus, methods and/or systems pertaining to convective cooling passages, especially as they might be used in the hot-gas path components of gas turbine engines. Note that, in part, the present invention will be described in relation to cooling the airfoils of rotary or gas turbine engines. This is exemplary only. As one of ordinary skill in the art will appreciate, the apparatus, methods, and/or systems described herein may be used more generally, for example, in any application where it is desired that heat be exchanged from a structure with a hollow passage to a working fluid that is flowing therethrough. Of course, as one of ordinary skill in the art will appreciate, there are many industrial applications that require heat exchange of this nature.
The airfoils of turbines, compressors, fans and the like, and particularly the rotor blades and stator blades of jet engines or gas turbine engines, generally are formed with internal hollow passages through which a cooling air is directed to convectively cool the internal walls of the passages. One prior art approach to increase the convective heat transfer between the cooling fluid and the internal walls of the blades has been to provide turbulence promoters within the internal cooling passages to interrupt the boundary layer growth of the cooling fluid adjacent the internal walls. By producing turbulent flow adjacent the internal wall surfaces, an improvement in heat transfer from these surfaces to the cooling fluid can be realized. Examples of turbulence promoters are disclosed in U.S. Pat. Nos. 4,627,480 and 5,704,763, the specifications of which are incorporated herein by reference.
Generally, the prior art in this technology area includes turbulence promoters that extend from the walls of the cooling passage into the flow field. One drawback associated with conventional turbulence promoters or turbulence generators is the creation of a large loss in the pressure of the cooling fluid as it passes over or through the turbulence generator baffles or ports defined within the cooling fluid passages. These large pressure drops may be compensated for by increasing the cooling fluid pressure and/or increasing the cooling fluid flow rates. This compensation, however, may detract from turbine engine performance and efficiency as the engine must provide additional bypass air that otherwise would be used for combustion. Moreover, this air dilutes the temperature of the gasses exiting the combustor and thus decreases the turbine rotor inlet temperature, which further reduces engine performance.
Accordingly, a need exists for a turbulence generator that avoids creating large pressure losses in the cooling fluid as it flows over wall surfaces being cooled. A need also exists for a coolant flowpath configuration which concentrates a flow of high velocity cooling fluid along localized portions of the flowpath wall surfaces so as to promote the creation of turbulent flow within the cooling fluid in order to disrupt boundary layer growth and enhance heat transfer.